In processes for producing synthetic hydrocarbonaceous products by pyrolysis from hydrocarbon-bearing materials, such as from oil shale or tar sands, a substantial amount of hot mineral residue is produced which must be disposed of. It is generally desirable to substantially lower the temperature of this residue prior to disposal both to aid in handling and to recover the heat from the residue which might otherwise be lost. Heat recovery from such materials presents special problems due to the nature of the residue and the large volume of material that must be handled. For example, the mineral residue remaining following the pyrolysis of oil shale contains a wide range of particle sizes varying from a fine powder (perhaps 150 microns) to fairly coarse granules (0.25 inches). In addition, since a ton of oil shale must be processed to obtain about 10 to 35 gallons of shale oil, a large volume of mineral residue must be handled. Conventional heat exchanges, such as shallow fluidized beds, have severe limitations when applied in processes of this type.
An efficient heat exchanger for use in a retorting process of this nature must be able to handle a large volume of material composed of a diversity of particle sizes and efficiently transfer the heat from the solid residue to a desired heat transfer fluid. The relatively long residence times required for efficient heat transfer is contrasted against the need to move enormous amounts of hot residue. For example in a commercial plant producing 100,000 barrels of oil per day approximately 300,000 tons of raw shale (assuming 20 gallons per ton of shale) must be processed per day. Since the inorganic component of the shale constitutes about 80% by weight of the raw shale, the magnitude of this problem becomes apparent.